This invention relates to the use of polymers of fumaric acid for the control or inhibition of the deposition of scale from water containing scale forming impurities, to processes for their synthesis and to polymeric intermediates of mono or dialkyl fumarate.
When natural waters and many man-made aqueous systems containing dissolved salts are used for distillation, heating or cooling purposes, the salts become insoluble and are deposited as scale on the heat transfer surfaces. The scaling, in turn, cuts down or destroys heat transfer and eventually causes failure of the equipment. In general, the mineral scale salts are derived from alkaline earth and other metal cations such as calcium, strontium, barium, magnesium, iron, lead and the like and anions such as bicarbonate, carbonate, sulfate, oxide, hydroxide, sulfide, phosphate, silicate, fluoride, chloride, bromide and the like. When deposited as scale, they appear in several forms or structures: adherent deposits formed directly on surfaces and non-adherent precipitated materials. Factors influencing scale formation include inverse temperature solubility of the various salts, the tendency of the salts to supersaturate and precipitate as the water is evaporated and the complex inorganic chemistry of the mineralized water, for example, its salt content, alkalinity, gegenion content and temperature among others.
A number of additives have been proposed as inhibitors of scaling. Among them are polycarboxylic acids, such as polyacrylic acid, polymaleic acid and polymethacrylic acid. Use of the carboxylic acid polymers in lower than the stoichiometric amount required to chelate the metallic ions present in the aqueous system has been shown to reduce effectively the tendency of the salts to deposit on heat transfer surfaces. This is termed the threshold effect and is accomplished in part by adsorption of the polymers onto the crystal nuclei as they are formed thereby suppressing further growth or adherence.
Accordingly, an object of the invention is to provide a method of inhibiting the deposition of scale on heat transfer surfaces such as those present in steam generators, desalination plants, cooling equipment, boilers and the like by use of an antiscaling agent in a threshold amount.
The polymerization of fumaric acid or its mixture with other monomers has been characterized as hard to achieve. Homopolymerization usually will not occur with any great facility and copolymerization incorporating more than 50 percent fumaric acid is difficult.
Accordingly, another object of the invention is to provide a process for the polymerization of fumaric acid and its admixtures with other monomers that is efficient, works in high yield and produces polymers of low to medium molecular weight.
The objects of the invention are met by use of novel polymers of fumaric acid which effectively inhibit scaling in such applications, by a novel method for their synthesis that employs esters of fumaric acid and by the polymeric intermediates of that synthesis.